Goodwin h



Patented Jan. 3,1928.

UNlTED STATES PATENT OFFICE.

GOODWIN H. HOWE, OF SCHNECTAJDY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TREATMENT OF METALS.

80 Drawing.

My invention relates to the art of treating metal so as to protect them against the effects of oxidation and other corrosive agencies, and has for its object the production of a coating upon a metal normally subject to corrosive actionor a condition within the metal such that it is capable of withstanding the oxidizing and corrosive influence without harmful effect.

My invention relates more specifically to the treatment of Such metals as iron, steel and copper, which readily oxidize at elerated temperature. It is now well known that these metals may be very effectively pro- ]5 tected by treating the surface with aluminum so as to cause the aluminum to alloy with the foundation metal. The trade name for this treatment of metal is calorizing.

This fundamental idea is disclosed in a patent to Tycho Van Aller No. 1,155,974 dated October 5, 1915. According to the. Van

Aller process, the article to be treated is brought into contact with aluminum powder at a proper temperature and under conditions which prevent oxidation of the metallic article, the treatment taking place in a closed oven which slowly rotates. After being thus treated for a proper length of time,

which may be about two hours, the article is fired at a temperature of between 700 and 800 C. for 15 or 20 minutes. More recently it has been found that a similar result may be obtained by dipping the article under proper conditions,-in molten aluminum and then firing. Examples of this process will be found in patents to Anseleno Ortez 21,409,017, William J. Keep #1,456,274,

Christian Dantsizen #1,381,085 and others.

These processes, .while very satisfactory, are

more or less limited in their application to articles of certain shapes and sizes. Ob-

' viously, it would be impracticable to treat very large, irregular shaped articles by the Van Aller process and, while it is possible to provide a ver large bath of molten aluminum for the ipping process, it will be obvious that there are likewise limitations to this process. Furthermore, the maintenance of a large bath of molten is expensive and some metals, such as non-ferrous metals, may be injured or even dis solvedin such abath.

It has been realized for uite some time that if the aluminum could e applied as a paint is applied, this field of protection of Application filed April 1, 1925. Serial m. 10,999.

metals would be greatly broadened. This would result not only from the wider application by reason of the increased dimensions of the articles which could be treated, but, also because of the decreased cost of operation. Attempts have been made to use.

the ordinary aluminum paint of commerce and other paints containing aluminum but these have all failed to produce the desired result. One of the reasons for this failure is that these paints all contain solid matter which interferes with the penetration of the aluminum into the article. Furthermore, ordinary aluminum paint aflords no protection against oxidation during firing. I have found that in order that the aluminum shall penetrate the article during firing, it is essential that the aluminum shall be in contact with a clean surface and provision should be made to prevent oxidation of the aluminum and, also of the foundation metal while the penetration is taking place during firing. I u

have also found a'way of causing aluminum powder to adhere to the clean surface of the foundation metal under conditions which will permit and cause the aluminum to penetrate. In other words, I have found a way of applying the aluminum in the way paint is applied and in a cold condition and at the same time produce a product which is equal, if not superior, in quality to that produced by the powder and dipping processes above 7 referred to.

In carrying out my invention I .em loy a mixture of aluminum powder, prefera ly of the granular form, with a suitable binder. Ordinary commercially pure aluminum may be used, such as 99% pure aluminum. I have found that certain grades of nitrocellulose which are soluble in either amyl acetate or 'wood alcohol form, when so dissolved, at solution, which is admirably adapted for the purpose of acting as a binder for the aluminum powder in applying it to the article;

Such a solution is known in commerce under the name pyroxylin. The properties of this solution which make it so desirable for my purpose are as follows: First, it wets and rmly adheres tometals; second, its solvents and thinners-evaporate rapidly and leave the nitrocellulose which acts as a binder; third, the nitrocellulose which is left as a binder volatilizes before a temperature is reached which will cause the aluminum to penetrate the foundation metal and leaves only from v to 2% ash, about half of which is silica,

, drogen but I have found that with certain here which in such small quantities is harmless; fourth, it is non-hydroscopic.

The surface of. he article is first thoroughly cleaned either by sand blasting or pickling. A mixture made of aluminum powder and this solution may then be applied in the ordinary way of applying paint. It may be applied with a brush, or by properly thinning with the solution it maybe sprayed on. I have even found that every satisfactory result may be obtained by dipping the article in a bath of this cold mixture. The mixture may also be ap lied in the form of paste. It might remains in suspension in this solution surprisingly well, although 'it will probably be desirable to provide means for stirring when the mixture is being used in large quantities. The coating should be made as even as possible and this can be done very easily as the mixture has the property of being very readily spread. When an even and continuous coatlng has been applied to the article, it is dried. This may be hastened by placing the coated article in an oven for about 15 minutes'at a temperature of from C. to 100 C.' After drying it will be found that the aluminum is quite firmly adherent, at least it cannot be rubbed off easily, and the article may be handled without in'ury to the coating. Of

'course, in this con ition it may be injured by .contact with a hard object and may even be scratched with the "finger nail, but .the coatingwill not be rubbed off by the ordinary contact with the hand. Further coatings may be applied until the desired thickness is obtaine *The article is now fired. This may, if desired, .be done in an atmosphere of hymaterials, such as the ferrous metals, as good results are "obtained by firing in the open air. When copper is being treated it is preferable to fire in ahydro en atmosphere. This brings out one o the chief values of the mtrocellulose solution. It

binds together the fine granules of aluminum an by excluding any appreciable amount of oxy en, allows an uncontaminated alloy to orm. In the case of iron the firing is done at 7 50" -900 C. for about an hour after which the article is removedand left in the open air to cool. 00 per should be fired at a temperature of a out 800C. from 5 to 10 minutes after the article has been heated. to that temperature.

'With iron lower temperaturesmay be used if the time of firing is increased, and this is true to some extent with copper.

The articles thus'treated have a protec-' tive coatin which insome respects is superior to t at producedz by the powder and e noted that the aluminum powder.

made by mixing 40 keeping the protected area, the result of which is that an unprotected area does not grow andeffect, protective areas as has been found to be the case with the other methods of treatment referred to. This point is-illustrated by the following experiment. A

paste was made of the proper consistency to form drops with good outline detail. drops of the material were placed upon several thick test pieces of iron and fired in air at 750900 C. The test pieces were then placed in a furnace at about 1000 C. and run for three days. Morning and night they were removed from the furnace,

allowed to cool and the loose scale removed.

At the end of three days the pieces were burned to destruction with the exception of the spots covered by the drops which re mained intact with the outlines still well defined. 1

The following test which demonstrated how firmly the coating adheres to the founby this severe bending. This test brings out one of the very important features ofthis new method of treatment, viz, that it may be used .for treating spots or areas as,

for instance, portions which cannot be fired in the usual way, as well as for repair or patch work.

. As to the particular materials and proportions, I have found that a goodpaste is grs. of granular aluminum with 25 c. c. o 6 oz. pyroxylin solution. For spraying, the following was worked out for use with a DeVilbiss, type D, spray gun: 40 gm. granular aluminum 2 benzol, 5 c. c."amylaceta I This mixture sprays well, forms an adherent coating and there is little difiiculty in dipping I have found thata very fine granus lar aluminum is preferable. Thealuminum' powder should be fine enough 0 c. c. 6 oz. pyroxylin solution, 10 c.- c.

aluminum in suspension. For

a: through a 270 mesh screen to give-the results with .the dip ing process. flaked aluminum; pow er is used in whole orm part the coating thus obtained is not as good as where the anular aluminum power only is used. to the defree of fineness of the aluminum granules, have found th t'this' depends somewhatup n the nature tendency for the coating to absorb of the coating desired. For smooth coatings a'very fine mesh screen is preferable, while a coarser mesh appears to be better for a heavier and more resistant coating. A mixture of the two is often found desirable.

While I have specified certain materials and proportions thereof which Ihave found to give very good results, it should be understood that my invention is in no sense limited in this respect. For instance, cellulose acetate might be used instead of cellulose nitrate, although I have not found it to give as good results, One of the reasons for this seems to be that the solvents for cellulose acetate are more hygroscopic than those employed with cellulose nitrate and hence do not evaporate as rapidly. Coatings will not, therefore, dry quickly unless heated, but if subjected to moist atmosphere before solvents have evaporated, there will be a moisture and precipitate out the cellulose. Another reason is that at the present time cellulose acetate costs much more than cellulose nitrate. As to the character of the aluminum,

I have stated above that the granular or' powdered material is preferable to flake aluminum, such as used in aluminum paints, and the reasons seem to be; first, there is less surface exposed and, consequently, less oxide in the metal; second, less solution is required for the mixture; third, the hardened coating is more durable, which is very important if the coated articles are not fired immediately. However, further experience might demonstrate some or all of these conclusions to be erroneous and I therefore wish it understood that my invention is not limited in respect to the particular materials employed or to their proportions or methods of handling except insofar as it is limited by the scope of the claims annexed hereto.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The process of protecting metallic articles from oxidation which consists in covering the surface of the article with a mixture of another metal in powdered form and a nitrocellulose binder, and then firing at a temperature which will cause the powdered metal to alloy with the metal of the article.

2. The process of protecting metallic articles from oxidation which consists in covering the surface to be protected with a powdered metal adapted to form an oxidation resisting alloy with the metal of the article, said powdered covering metal being applied at ordinary temperatures in combination with a cellulose derivative binder, and then firing at covering metal to alloy the article.

3. The process of protecting metallic articles from oxidation which consists in covering at ordinary temperatures the surface of the article with a mixture of aluminum powder and a liquid consisting of nitrocellulose and a volatile solvent, and then firing at a temperature which will cause the aluminum to alloy with the metal of the article.

4. The process of protecting metallic articles from oxidation which consists in cover ing the article with a coating composed of aluminum powder and a binder having a cellulose nitrate base, drying the coating,

with the metal of a temperature which will cause the.

then firing it at atemperature which will cause the aluminum to alloy with the metal of the article.

5. The process of protecting metallic articles from oxidation which consists in covering the articles at ordinary temperatures with a coating composed of aluminum powd8]. and a "liquid nitrocellulose binder which wets and firmly adheres to metals at ordi-' nary temperatures and 'volatilizes at higher temperatures, drying the coating and then firing at a temperature at which the aluminum alloys with the metal of the article, said temperature being above that at which the binder volatilizes.

In witness whereof I have hereunto set my hand this 31st day of March, 1925. 

